Judge in Bill Cosby Case Declares a Mistrial

• The exhausted jurors had been deliberating since Monday, sometimes for as much as 12 hours a day.

• The mistrial, which Mr. Cosby’s lawyers had supported, means that prosecutors will need to decide whether to retry Mr. Cosby on the charges at a later date.

The decision denied a measure of vindication either to Mr. Cosby or to the dozens of women who have accused him of assaulting them.

In their sixth day of deliberations, jurors sent word to Judge Steve T. O’Neill that they could not reach a unanimous verdict on the charges that in 2004, Mr. Cosby, one of the world’s best-known entertainers, drugged and assaulted Andrea Constand in his home near here.

The hung jury means that the Montgomery County District Attorney, Kevin R. Steele, must decide whether to retry the case. Once again, he will have to balance the fact that dozens of women who have leveled similar accusations at Mr. Cosby had looked to this case as likely the only chance to hold him criminally responsible, against the value of pursuing a 79-year-old defendant who is fighting blindness, whose career and reputation are in tatters, and for whom a prison term could amount to a life sentence.

Mr. Cosby reacted calmly to the decision, rubbing his face at one point, while Ms. Constand stared straight ahead. Mr. Steele announced in the courtroom that he planned on retrying the case.

“This is neither a vindication or a victory,” said Judge O’Neill who praised the jurors for their service and asked them not to discuss their deliberations. “They are yours and yours alone,” he said.

The case turned largely on the credibility of Ms. Constand, a former Temple University employee. She testified that the assault occurred in a visit to the home of Mr. Cosby, who was a Temple trustee, when she was 30 and he was 66. She said that Mr. Cosby gave her pills that he said were herbal, but that left her immobile and drifting in and out of consciousness. He has said that he only gave her Benadryl.

“I was jolted awake and I felt Mr. Cosby’s hand groping my breasts under my shirt,” she testified last week. “I also felt his hand inside my vagina moving in and out, and I felt him take my hand and place it on his penis and move it back and forth.”

Mr. Cosby was charged with three counts of aggravated indecent assault – penetration with lack of consent, penetration while unconscious, and penetration after administering an intoxicant without the subject’s knowledge. Each is a felony punishable by up to 10 years in state prison, though the sentences could be served concurrently.

The jury of 12 was composed of six white men, four white women, one black woman and one black man. They had reported being deadlocked on Thursday but then had resumed deliberations at the request of the judge. As it turned out the deliberations ended up taking longer than the presentation of evidence had.

In recent years, Mr. Cosby, 79, had admitted to decades of philandering, and to giving quaaludes to women to induce them to have sex, smashing the image he had built as a moralizing public figure and the upstanding paterfamilias in the wildly popular 1980s and ’90s sitcom “The Cosby Show.”

As a result, he avoided a grilling about those admissions, but he and his lawyers had insisted that his encounters with Ms. Constand were part of a consensual affair, not an assault.

The jury had first notified the judge of its deadlock late on Thursday morning. He instructed them to keep trying, giving what is known in Pennsylvania law as a “Spencer charge.”

“While you should not hesitate to re-examine your own views and change your opinion if you are convinced that your opinion is erroneous, do not feel compelled to surrender your honest belief as to the weight or effect of the evidence solely because of the opinion of your fellow jurors, or for the mere purpose of returning a verdict,” Judge O’Neill said. But the jury returned at roughly 10 a.m. to say that it remained divided, and the judge brought the trial to an end.

The mistrial leaves in limbo a large slice of American popular culture from Mr. Cosby’s six-decade career as a comedian and actor. For the last few years, his TV shows, films and recorded stand-up performances, one-time broadcast staples, have been considered too toxic to touch, and with the mistrial, they are likely to remain so.

Mr. Cosby’s supporters had hoped that a not-guilty verdict might tarnish the broader pool of accusations that have been leveled against him and stained his legacy. Several of the women have ongoing cases in which they have sued Mr. Cosby for slander after his representatives suggested that their accounts were fabrications. Several showed up in the courthouse to support Ms. Constand each day.

Ms. Constand took the witness stand last week as a proxy for all the women who have accused Mr. Cosby — including a few who attended the trial — often with details remarkably similar to Ms. Constand’s story.

Adding weight to the allegations was the revelation in 2015 that Mr. Cosby, in a 2005 lawsuit filed by Ms. Constand, had admitted securing quaaludes so women would have sex with him.

None of the other women’s accusations had resulted in prosecution — in many cases, too much time has passed — leaving Ms. Constand’s case as the only formal test of Mr. Cosby’s guilt. Prosecutors wanted to call a dozen of the accusers to testify in the trial, but Judge O’Neill allowed just one, Kelly Johnson, who testified that Mr. Cosby had drugged and assaulted her in 1996.

Jurors conceded during jury selection that they were aware of the claims. Mr. Cosby’s lead lawyer, Brian J. McMonagle, on Monday cited the “drumbeat” of highly publicized charges, saying that the case was more media frenzy than legal tribunal.

Mr. McMonagle insisted that Ms. Constand was lying about a consensual sexual relationship.

“They’ve been intimate,” he said in his closing. “Why are we trying to make it something it’s not?”

He conceded that Mr. Cosby is a flawed man, an unfaithful husband who shattered his fans’ illusions, and that revelations of his womanizing have overtaken his previous image as a genial comedian and beloved TV dad. But that is no crime, he said.

As if to show that he, too, was disappointed in Mr. Cosby — and perhaps offer the jury the catharsis of a public shaming — Mr. McMonagle pointed at his client during closing arguments and declared angrily, “You danced outside your marriage.” Turning to Mr. Cosby’s wife, Camille, who was making her first appearance at the trial and sitting in the front row, he added, “And you deserved better.”

Mr. Steele had also addressed Mr. Cosby directly, in a closing argument that lasted for more than two hours. He said that Mr. Cosby, a Temple University trustee and the university’s most famous alumnus, set his sights on Ms. Constand, an employee in the university’s athletic department.

“You ingratiated yourself into this woman’s life,” he said. “You treated her well. You paid her attention. And then you drugged her and you did what you wanted.”

The defense seized on inconsistencies in the version of events Ms. Constand gave when she went to the police the next year, and statements she made later on: She said the assault took place in March, 2004, after dinner at a restaurant, then said it occurred earlier, unconnected to the restaurant outing; she said the incident had been the first time she had been alone with Mr. Cosby in his home, then said it was the third time, and that she had rebuffed his sexual advances the first two times; she said she had minimal communication with him after the incident, then acknowledged many contacts.

“Ms. Constand was untruthful time and time and time again,” Mr. McMonagle told the jury. “There is one contradictory story after another.”

He questioned why an assault victim would have continued frequent contact with her assailant, and as evidence of a sexual relationship, he cited a trip Ms. Constand took to a resort to see Mr. Cosby perform, when she visited him in his hotel room.

“Why on earth would you go to Foxwoods casino in Connecticut after he has already unbuttoned your pants and put his hands down your pants?” Mr. McMonagle demanded.

During the trial, the prosecution called one expert who testified that victims’ accounts are often disjointed and inconsistent, and another who said that Benadryl, in a high dose, could be a powerful sedative.

Under cross-examination, Ms. Constand explained her lapses as innocent mistakes, and said her contacts with Mr. Cosby after the incident were mostly cursory, the unavoidable result of her job duties.

Mr. Steele told the jury that Mr. Cosby took away Ms. Constand’s ability to consent when he gave her the pills, that their later contacts were irrelevant, and that jurors should ignore what he said were myths about how sexual assault victims are supposed to behave.

When Ms. Constand’s mother called to confront Mr. Cosby roughly a year after the incident, he said, the defendant’s apology, and his offer to pay for her schooling, therapy and a trip to Florida, were evidence that he knew he had done something wrong.

“Andrea Constand’s own words, just what she told you, should sustain a conviction in this case,” Mr. Steele said. “But under the defendant’s own words, you must convict.”

The prosecution had rested its case a week ago, and the defense presented a case Monday that lasted just six minutes — in essence telling the jury that prosecutors had failed to prove anything, and that there was little or nothing left for them to rebut.

The defense team called just one witness, Sgt. Richard Schaffer of the Cheltenham Township Police, who interviewed Mr. Cosby and Ms. Constand after her initial complaint 12 years ago, and who testified last week as a prosecution witness. Mr. McMonagle questioned him briefly about a document he created in 2005, labeled “Questions for Andrea,” looking for clarification about elements of her account.

The defense chose not to summon to the witness stand Bruce L. Castor Jr., the former district attorney who in 2005 declined to file criminal charges against Mr. Cosby. Though the prosecutors did not know then of Mr. Cosby’s admission about giving women quaaludes, Mr. Cosby’s lawyers have repeatedly cited Mr. Castor’s decision not to prosecute as an indication that the current case is unfounded.

But calling Mr. Castor would have been a gamble, given his mixed views of the case. He said in a 2014 interview that he did not think, in 2005, that there was enough evidence to persuade a jury of Mr. Cosby’s guilt, “despite the fact that I thought Cosby was guilty of some improper behavior.”